coltivirus

Coltivirus (Colorado tick fever virus) is a segmented double-stranded RNA virus belonging to the Reoviridae family. It is transmitted to humans via the bite of the wood tick, Dermacentor andersoni, in mountainous regions of the western US and Canada, typically during spring and summer months. After an incubation period of 3-6 days, patients develop an abrupt onset of fever, chills, severe myalgias, headache, retro-orbital pain, and photophobia. A classic and distinctive feature is the 'saddleback' or biphasic fever pattern, where fever resolves after 2-3 days then recurs for another few days. Leukopenia and thrombocytopenia are common laboratory findings. The virus has tropism for erythroid precursor cells, leading to prolonged viremia within red blood cells (up to weeks), which is unusual among viral infections and can complicate blood donation screening. Rash occurs in a minority of patients. Rarely, complications include aseptic meningitis, encephalitis, or hemorrhagic fever, particularly in children. Diagnosis is largely clinical, supported by exposure history and can be confirmed via RT-PCR, viral culture, or serology. Treatment is supportive (antipyretics, hydration, avoiding aspirin due to bleeding risk); no specific antiviral therapy or vaccine exists. Prevention focuses on tick avoidance measures (repellents, protective clothing, prompt tick removal). It's a high-yield board topic due to its association with a specific tick vector, geographic distribution, and the unique biphasic fever pattern with erythrocyte-associated viremia, distinguishing it from other tick-borne illnesses like Rocky Mountain spotted fever (bacterial, different vector-associated rash pattern) or ehrlichiosis.